Apples or Bananas
When I see 40% conversion rate that immediately alerts me. Two digit conversions (10% to 40%) are very uncommon for AdWords. Your example sounds more like a soft or micro conversion (eg. click on a link), which can be helpful to track but in most cases is just a partial goal achievement. The range for hard conversions (purchase, lead, etc.) is generally around the lower 1 digit percentage (0.5% up to 5%), all depending upon industry, channel, campaign, competition, etc. I read that average macro conversions can go up to 10% or 12% in certain industries, but I personally have never seen that in real life.
So when you compare conversion rates do try to find a very similar case.
Micro and macro conversions: https://support.google.com/analytics/answer/2665457?hl=en
The following explanation fits your question and looks quite objective: https://www.quora.com/What-is-the-average-PPC-conversion-rate-for-the-healthcare-industry-on-Google
The range of conversion rates can highly differ on campaign type (search, display) and keywords / content. Normally the campaigns with very high conversion rates will give you only a low volume of conversions. If you need volume you’ll have to deal with lower conversion rates.
- Forms: For the contact form I have seen much better conversion rates if the form was above the fold. Also a form conversion can be tracked quite well.
- Phone numbers: Same as forms the phone numbers need to be above the fold. But phone conversions can’t be tracked so easy. Google offers a method to have a redirect number installed on the landingpage which can be tracked more accurately but is more complex to set up.
- Above the fold: Basically the value proposition and conversion goal need to be above the fold.